Generally, a wireless communication system includes a portable subscriber station (PSS), a radio access station (RAS), a repeater and a contents server. The portable subscriber station (PSS) can use communication services, such as call connection, digital broadcast, digital media downloading, uploading, and so on, via the radio access station (RAS) in a wireless net. The contents server manages users of the portable subscriber station (PSS) and provides necessary contents to the portable subscriber station (PSS). If there is the radio access station (RAS) without the repeater in a region, a signal reception becomes poor in the region. The poor signal reception is compensated with the repeater.
Since there exists a limitation of available frequencies in a wireless communication system, the frequencies are assigned to the radio access stations (RAS) depending on their services. Moreover, the frequencies are used in duplicate by separating the radio access stations (RAS) from each other to avoid interference between adjacent radio access stations (RAS). In this case, a plurality of sectors in a cell of each radio access stations (RAS) may use different frequencies. The plurality of sectors may use frequencies at the same time.
FIG. 1 is a schematic view showing a conventional radio access station (RAS) using a plurality of frequency bands. In other word, FIG. 1 shows a frequency reuse factor-3 (FRF-3) type scheme. In more detail, in the conventional wireless communication system, a region, which one radio access station (RAS) covers, is divided into a plurality of sectors. The region is defined as a cell. Namely, the region is divided into first, second and third sectors 110, 120 and 130, and the first, second and third sectors 110, 120 and 130 constitute the cell. Then, different three frequency bands are assigned each sectors, and thereby providing communication services between the radio access station “RAS” and the portable subscriber stations (PSS) (not shown) in each sectors 110, 120 and 130. The radio access station “RAS” communicates the portable subscriber stations (PSS) in the first sector 110 using a first frequency band “FA1”. The radio access station “RAS” communicates the portable subscriber stations (PSS) in the second sector 120 using a second frequency band “FA2”. The radio access station “RAS” communicates the portable subscriber stations (PSS) in the third sector 130 using a third frequency band “FA3”. In this case, each of the first, second and third sectors 110, 120 and 130 transmits the traffics using carrier waves respectively assigned to different frequency bands “FA1”, “FA2” and “FA3”.
In the conventional wireless communication system shown in FIG. 1, since each sectors uses different frequency bands, there are few interference in border region between adjacent sectors and between adjacent cells of adjacent radio access stations “RAS”. Accordingly, there is no problem of decrease of a carrier to interference and noise ratio (CINR), and cell coverage increases. However, because each sector uses a single frequency band, there is a relatively lower system capacity than a wireless communication system shown in FIG. 2.
FIG. 2 is a schematic view showing a conventional radio access station (RAS) using an identical frequency. In other word, FIG. 2 shows a frequency reuse factor-1 (FRF-1) type scheme. In the wireless communication system shown in FIG. 2, all sectors in each radio access station “RAS” uses an identical frequency “FA” to transmit the traffics. Accordingly, the system capacity is improved. Furthermore, as shown in FIG. 3, one control message following a preamble and a frame control header “FCH” in a data frame is transmitted repeatedly. The one control message may be transmitted six times.
However, in the wireless communication system in FIG. 2, signal interference at a border region 210 between adjacent sectors and a border region 220 between adjacent cells of adjacent radio access stations “RAS” is easily caused. Namely, since every sector and every cell uses identical frequency band to provide communication services in the wireless communication system, signal interference at the border region 210 between the adjacent sectors and the border region 220 between the adjacent cells of the adjacent radio access stations “RAS” is easily caused. As a result, a carrier to interference and noise ratio (CINR) of the portable subscriber station (PSS) decreases, and it is difficult to provide communication services. Communication service quality is deteriorated.